Mobile communication systems are evolving to provide UEs with high-speed and large-capacity services. Representative examples of such mobile communication systems include a High-Speed Downlink Packet Access (HSDPA) mobile communication system, a High-Speed Uplink Packet Access (HSUPA) mobile communication system, a Long-Term Evolution (LTE) mobile communication system, a Long-Term Evolution-Advanced (LTE-A) mobile communication system, an Institute of Electrical and Electronics Engineers (IEEE) 802.16m mobile communication system, and the like.
The LTE mobile communication system has been developed to efficiently support high-speed wireless packet data transmission, and can maximize the capacity of a mobile communication system by utilizing various Radio Access (RA) technologies. The LTE mobile communication system proposes a Circuit Switched FallBack (CSFB) scheme capable of using both a circuit scheme and a packet scheme to support a voice call service. The CSFB scheme uses a Circuit-Switched call (CS call) together with Voice over LTE (VoLTE). Here, VoLTE supports voice calls using a packet scheme, and the CS call supports voice calls using a circuit scheme and was used by the conventional 2G/3G mobile communication system until VoLTE came to be stably served.
Meanwhile, when multiple UEs simultaneously attempt to access a network through a particular base station, excessive packet data is transmitted to the particular base station, which causes the occurrence of a congestion status, whereby the performance of the relevant network is reduced. For example, when due to the occurrence of an emergency situation such as a disaster, at least one base station becomes inoperative. This may occur, for example, when many people are crowded in a particular area, so that excessive network access through some base stations may occur.